The present invention relates to limited slip differentials, and more particularly, to such differentials of the type in which the means for retarding differentiating action may be modulated in response to an external input signal.
Limited slip differentials of the type to which the present invention relates typically include a gear case defining a gear chamber, and disposed therein, a differential gear set including at least one input pinion gear, and a pair of output side gears. A clutch pack is typically disposed between at least one of the side gears, and an adjacent surface of the gear case, such that the clutch pack is operable to retard, or even prevent, relative rotation between the gear case and the one side gear. Although the present invention is not limited to limited slip differentials in which the clutch pack is disposed axially between one of the side gears and an adjacent surface of the gear case, the present invention is especially advantageous when used in connection with a limited slip differential having such an arrangement, and the invention will be described in connection therewith.
In many limited slip differentials, some sort of actuating mechanism is provided to actuate or move the clutch pack from its disengaged condition to an engaged condition.
One of the current trends in the field of vehicle traction modifiers involves the desire to be able to actuate the clutch pack in response to an external input signal, rather than only in response to the sensing of a predetermined speed differential, as has typically been the case in the prior art.
One prior art approach to providing the ability to modulate a limited slip differential has been by the application of a varying hydraulic pressure to a piston disposed in engagement with the clutch pack, such that the "bias torque" (i.e., the amount of torque transferred from the low traction wheel to the high traction wheel as a result of clutch pack engagement) would vary with variations in hydraulic pressure. Such a limited slip differential is illustrated and described in U.S. Pat. No. 3,138,970. Differentials made in accordance with the teachings of U.S. Pat. No. 3,138,970 have not become commercially successful, primarily because the overall design is excessively complex, requiring several hydraulic lines, and expensive and complex rotating hydraulic seal arrangements.
U.S. Pat. No. 4,644,823 discloses a limited slip differential in which a hydraulic signal is applied to a piston-like member of a bearing assembly, such that hydraulic pressure biases the entire bearing assembly, and several other members, in an axial direction, eventually loading the differential clutch pack. Again, the device of the referenced patent is excessively complex, such that it would require major redesign of any of the commercially available limited slip differentials, and most likely, substantial redesign of the surrounding differential housing, which is particularly unacceptable to the vehicle original equipment manufacturers.
U.S. Pat. No. 4,805,486 discloses a limited slip differential having a clutch pack in which loading of the clutch pack occurs in response to ramping of a ball-ramp actuator which is disposed external to the differential case. Ramping of the ball ramp actuator is initiated by rotation of a servo-motor, and by means of a parallel-shaft gear train, which also would require substantial redesign of the surrounding differential housing.